class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ret = 0;
        for (int i = 0; i < 32; i++)
        {
            int sum = 0;
            for (auto& e : nums)
            {
                if (((e >> i) & 1) == 1)
                    sum++;
            }
            sum = sum % 3;
            if (sum == 1)
                ret = ret | (1 << i);
        }
        return ret;
    }
};